1. Field of the Invention
The present invention relates to an engine for a vehicle including a crankshaft room for housing a crankshaft and a transmission room partitioned from the crank room by a partition wall, the transmission room housing a gear transmission having a gear train for backward movement and reserving oil of the engine.
2. Description of the Related Art
FIG. 9 shows an example of above mentioned type engine for a vehicle. In FIG. 9, a crankcase 300 is partitioned into a front crank room 301 and a rear transmission room 302 by a partition wall 303 having a predetermined height. The crankshaft room 301 houses a crankshaft 305a. The transmission room 302 houses a gear transmission having a gear train 305 for backward movement. Further, the transmission room 302 reserves oil in a lower portion thereof.
The gear train 305 for backward movement has a low gear 311 provided on an input shaft 310 of the gear transmission, a reverse driven gear 313 provided on an output shaft 312 of the gear transmission, and reverse idle gears 315 and 316 provided on a reverse idle shaft 317 and engaged with the low gear 311 and the reverse driven gear 313 respectively. The input shaft 310 is arranged between the crankshaft 305 and the output shaft 312 in a forward and backward direction (i.e. front to back) of the vehicle. The reverse idle shaft 317 is arranged above the input shaft 310 and the output shaft 312.
FIG. 10 is an enlarged view in section taken along line X-X of FIG. 9. The reverse idle shaft 317 arranged above the input shaft 310 is extended over the entire lateral width (right and left width) of the crankcase 300 and is rotatably supported by the left and right side walls of the crankcase 300 via bearings 322. The reverse idle gears 316 and 315 are formed on the left and right ends of the reverse idle shaft 317.
As shown in FIGS. 9 and 10, the input shaft 310 is arranged between the crankshaft 305 and the output shaft 312 from front to back, and the reverse idle shaft 317 is arranged above the output shaft 312 and the input shaft 310. In such a configuration, the size of the engine in a vertical direction is increased, as seen in the crankshaft direction. Further, since the reverse idle shaft 317 is arranged above the output shaft 312 and the like, a top wall of the crankcase 300 protrudes upward, thereby, the arrangement space for engine parts e.g., a starter motor, arranged on a top surface of the crankcase 300 is limited. Furthermore, the size of the engine for the vehicle in the vertical direction is increased so that a ground clearance of the vehicle is decreased.
To address such problems, the present inventors have developed an engine for a vehicle, as disclosed in U.S. Pat. No. 6,799,485B1, wherein the reverse idle shaft is arranged below the input shaft of a gear transmission, and the reverse idle gear mounted on the reverse idle shaft is arranged across a transmission case and the generator case.
However, in the case of above-mentioned engine, so that the reverse idle gear can be arranged across the transmission case and the generator case, a notch for inserting the reverse idle gear thereinto must be formed in a partition wall for partitioning both the cases, as a result, both the cases communicate with each other through the notch. An oil reservoir (oil pan portion) must be formed in the transmission case to prevent backflow of the oil to the generator case through the notch. Therefore, it is difficult to make a crankcase having a compact transmission case and maintain a sufficient amount of the oil in the oil reservoir. The notch in the partition wall affects the strength of the crankcase around the reverse idle gear. This also makes it difficult to make the crankcase compact.